Magnetic recording media are widely used in various applications, e.g., in hard disk form, particularly in the computer industry for storage and retrieval of large amounts of data/information in magnetizable form. Such media are conventionally fabricated in thin film form and are generally classified as “longitudinal” or “perpendicular”, depending upon the orientation (i.e., parallel or perpendicular) of the magnetic domains of the grains of the magnetic material constituting the active magnetic recording layer, relative to the surface of the layer.
A portion of a conventional thin-film, longitudinal-type recording medium 1 utilized in disk form in computer-related applications is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically of glass or a metal, e.g., an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (“DLC”), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium 1, the magnetic layer 13 is locally magnetized by a write transducer or write head (not shown in FIG. 1 for simplicity) to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field applied by the write transducer is greater than the coercivity of the recording medium layer 13, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field applied by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
A typical recording system 20 utilizing a thin-film, vertically oriented, perpendicular-type magnetic medium 1′ is illustrated in FIG. 2, wherein reference numerals 10, 11, 12A, 12B and 13′, respectively, indicate the substrate, plating layer, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular-type magnetic medium 1, and reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head 6. Relatively thin interlayer 12B (also referred to as an “intermediate” layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 12A and the hard recording layer 13′ and (2) promote desired microstructural and magnetic properties of the hard recording layer. As shown by the arrows in the figure indicating the path of the magnetic flux φ, flux φ is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through vertically oriented, hard magnetic recording layer 13′ (which, as is known, may comprise a Co-based alloy, an iron oxide, or a multilayer magnetic superlattice structure) in the region above single pole 7, entering and travelling along soft magnetic underlayer 12A for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer 13′ in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 2, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium 1. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer 14, such as of a diamond-like carbon (DLC) formed over hard magnetic layer 13′, and a lubricant topcoat layer 15, such as of a perfluoropolyethylene material, formed over the protective overcoat layer. As with the longitudinal-type recording medium 1 shown in FIG. 1, substrate 10 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Al—Mg having an Ni—P plating layer 11 on the deposition surface thereof, or substrate 10 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; soft underlayer 12A is typically comprised of an about 500 to about 4,000 Å thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, etc.; thin interlayer 12B typically comprises an up to about 100 Å thick layer of a non-magnetic material, such as TiCr; and hard magnetic layer 13′ is typically comprised of an about 100 to about 250 Å thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, and B, iron oxides, such as Fe3O4 and δ—Fe2O3, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 Å thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, and Pt, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 Å thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
A typical contact start/stop (CSS) method employed during use of disk-shaped media involves a floating transducer head gliding at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between mutually sliding surfaces of the transducer head and the disk. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head is freely movable in both the circumferential and radial directions, thereby allowing data to be recorded and retrieved from the disk at a desired position in a data zone.
Adverting to FIG. 3, shown therein, in simplified, schematic plan view, is a magnetic recording disk 30 (of either longitudinal or perpendicular type) having a data zone 34 including a plurality of servo tracks, and a contact start/stop (CSS) zone 32. A servo pattern 40 is formed within the data zone 34, and includes a number of data track zones 38 separated by servo tracking zones 36. The data storage function of disk 30 is confined to the data track zones 38, while servo tracking zones 36 provide information to the disk drive which allows a read/write head to maintain alignment on the individual, tightly-spaced data tracks.
Although only a relatively few of the servo tracking zones are shown in FIG. 3 for illustrative simplicity, it should be recognized that the track patterns of the media contemplated herein may include several hundreds of servo zones to improve head tracking during each rotation of the disk. In addition, the servo tracking zones need not be straight radial zones as shown in the figure, but may instead comprise arcs, intermittent zones, or irregularly-shaped zones separating individual data tracks.
In conventional hard disk drives, data is stored in terms of bits along the data tracks. In operation, the disk is rotated at a relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which radially positions the head on the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk, i.e., over a data track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above that track. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks. Many actuator arms are rotatable, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm about an axis of rotation. Alternatively, a linear actuator may be used to move a magnetic head assembly radially inwardly or outwardly along a straight line.
As has been stated above, to record information on the disk, the transducer creates and applies a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium, and grains of the recording medium at that location are magnetized in a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the magnetic field is removed. As the disk rotates, the direction of the writing magnetic field is alternated, based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, eight “bits” typically form one “byte” and bytes of data are grouped as sectors. Reading or writing a sector requires knowledge of the physical location of the data in the data zone so that the servo-controller of the disk drive can accurately position the read/write head in the correct location at the correct time. Most disk drives use disks with embedded “servo patterns” of magnetically readable information. The servo patterns are read by the magnetic head assembly to inform the disk drive of track location. In conventional disk drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a “servo burst”. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is a time consuming process.
Commonly assigned U.S. Pat. No. 5,991,104 to Bonyhard, the entire disclosure of which is incorporated herein by reference, discloses a method for forming a servo pattern in a magnetic disk, comprising the steps of:                1) aligning a magnetic disk immediately adjacent a master servo-writer medium, the latter having a greater magnetic coercivity than the former, wherein the servo-writer medium has a master servo pattern magnetically stored thereon which defines a plurality of concentric tracks;        2) applying a magnetic assist field to the aligned master servo-writer medium and magnetic disk, the magnetic assist field having a substantially equal magnitude at all tracks on the aligned master servo-writer medium and magnetic disk; and        3) rotating the aligned master servo-writer medium and magnetic disk relative to the magnetic assist field.        
However, the above-described method incurs several drawbacks associated with its implementation in an industrially viable manner. Specifically, a “one-of-a-kind” master writer with a very high write field gradient is necessary for writing the requisite high intensity, master magnetic servo pattern onto the master disk, and a complicated means for rotating the aligned master servo-writer disk and “slave” workpiece magnetic disk is required, as is a complex system for controlling/regulating/rotating the intensity (i.e., magnitude) and directions of the magnetic assist field.
Commonly assigned, co-pending U.S. patent application Ser. No. 10/082,178, filed Feb. 26, 2002, the entire disclosure of which is incorporated herein by reference, discloses an improvement over the invention disclosed in the aforementioned commonly assigned U.S. Pat. No. 5,991,104, and is based upon the discovery that very sharply defined magnetic transition patterns can be reliably, rapidly, and cost-effectively formed in a magnetic medium containing a longitudinal or perpendicular type magnetic recording layer: (1) without requiring expensive, complicated fabrication of a master disk (alternatively referred to as a “stamper/imprinter”) having a contacting (i.e., imprinting) surface comprised of a plurality of magnets or magnetized areas corresponding to the desired magnetic transition pattern to be formed in the magnetic disk (i.e., “slave”), and (2) without requiring rotation of the master/slave pair in a magnetic assist field of variable strength and polarity.
Specifically, the invention disclosed in co-pending, commonly assigned U.S. patent application Ser. No. 10/082,178 is based upon recognition that a stamper/imprinter (“master”) comprised of a magnetic material having a high saturation magnetization, Bsat, i.e., Bsat≧about 0.5 Tesla, and a high permeability, μ, i.e., μ≧about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, can be effectively utilized as a “master” contact mask (or “stamper/imprinter”) for “imprinting” of a magnetic transition pattern, e.g., a servo pattern, in the surface of a magnetic recording layer of a magnetic medium (“slave”), whether of longitudinal or perpendicular type. A key feature of the invention is the use of a stamper/imprinter having an imprinting surface including a topographical pattern, i.e., comprised of projections and depressions, corresponding to a desired magnetic transition pattern, e.g., a servo pattern, to be formed in the magnetic recording layer. An advantage afforded by the invention is the ability to fabricate the topographically patterned imprinting surface of the stamper/imprinter, as well as the substrate or body therefor, of a single material, as by use of well-known and economical electro-forming techniques.
According to the disclosed invention, the magnetic domains of the magnetic recording layer of the slave medium are first unidirectionally aligned (i.e., “erased” or “initialized”), as by application of a first external, unidirectional magnetic field Hinitial of first direction and high strength greater than the saturation field of the magnetic recording layer, typically≧2,000 and up to about 20,000 Oe. The imprinting surface of the stamper/imprinter (master) is then brought into intimate (i.e., touching) contact with the surface of the magnetic recording layer (slave). With the assistance of a second externally applied magnetic field of second, opposite direction and lower but appropriate strength Hre-align, determined by Bsat/μ of the stamper material (typically≧100 Oe, e.g., from about 2,000 to about 4,500 Oe), the alignment of the magnetic domains at the areas of contact between the projections of the imprinting surface of the stamper/imprinter or at the areas facing the depressions of the imprinting surface of the stamper/imprinter and the magnetic recording layer of the medium to be patterned (slave) is selectively reversed, while the alignment of the magnetic domains at the non-contacting areas (defined by the depressions in the imprinting surface of the stamper/imprinter) or at the contacting areas, respectively, is unaffected, whereby a sharply defined magnetic transition pattern is created within the magnetic recording layer of the medium to be patterned (slave) which essentially mimics the topographical pattern of projections and depressions of the imprinting surface (master). According to the invention, high Bsat and high μ materials are preferred for use as the stamper/imprinter in order to: (1) avoid early magnetic saturation of the stamper/imprinter at the contact points between the projections of the imprinting surface and the magnetic recording layer, and (2) provide an easy path for the magnetic flux lines which enter and/or exit at the side edges of the projections.
A stamper/imprinter for use in a typical application according to the disclosed invention, e.g., servo pattern formation in a disk-shaped, thin film, longitudinal or perpendicular magnetic recording medium, is formed according to conventional techniques, and comprises an imprinting surface having topographical features consisting of a pattern of well-defined projections and depressions corresponding to conventional servo patterns, as for example, disclosed in the aforementioned commonly assigned U.S. Pat. No. 5,991,104 the entire disclosure of which is incorporated herein by reference. For example, a suitable topography may comprise a plurality of projections having a height in the range from about 20 to about 500 nm, a width in the range from about 0.01 to about 1 μm, and a spacing of at least about 0.01 μm. Stampers/imprinters comprising imprinting surfaces with suitable surface topographies may be readily formed by a variety of techniques, such as electroforming onto a planar-surfaced substrate through an apertured, non-conductive mask, or by pattern formation in a planar-surfaced substrate by means photolithographic wet (i.e., chemical) or dry (e.g., plasma, sputter, or ion beam) etching techniques.
FIG. 4 illustrates a sequence of steps for performing magnetic transition patterning by contact printing of a perpendicular recording medium, e.g., medium 1′ depicted in FIG. 2 and comprised of a non-magnetic substrate 10 and an overlying thin layer 13′ of a perpendicular-type magnetic recording material (where plating layer 11, soft magnetic underlayer 12A, and non-magnetic interlayer 12B are omitted from FIG. 4 in order to not unnecessarily obscure the essential features/aspects of the present invention) is subjected to a DC erase or magnetic initialization process for unidirectionally aligning the perpendicularly oriented magnetic domains 13⊥ of magnetic recording layer 13′. Magnetic initialization of perpendicular medium 1′ is accomplished by applying a first, high strength, unidirectional DC magnetic initialization field Hinitial normal to the opposed major surfaces thereof, i.e., normal to the lower surface of substrate 10 and upper surface of magnetic recording layer 13′, wherein Hinitial≧coercivity of layer 13′ and is typically in the range from above about 2,000 to about 20,000 Oe.
According to the next step of the process sequence, a stamper/imprinter 16 composed of composed of a body of magnetic material having a high saturation magnetization, Bsat, i.e., Bsat≧about 0.5 Tesla, and a high permeability, μ, i.e., μ≧about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, and having an imprinting surface 17 having a topography comprised of a plurality of projections 18 and depressions 19 arranged in a pattern corresponding to a magnetic transition pattern to be formed in the surface of magnetic recording layer 13′, e.g., a servo pattern, is placed in intimate (i.e., touching) contact with the surface of layer 13′. By way of illustration only, a suitable topography for the imprinting surface 17 of a contact mask-type stamper/imprinter 16 for use in forming a servo pattern according to the invention may comprise a plurality of projections 18 having a height in the range from about 20 to about 500 nm, a width in the range from about 0.01 to about 1 μm, and a spacing (defining the depressions 19) of at least about 0.01 μm). A second, unidirectional DC magnetic re-alignment field Hre-align of direction reverse that of the DC magnetic initialization field Hinitial is then applied normal to the upper surface of stamper/imprinter 16 and the lower surface of substrate 10 of medium 1′, the strength of Hre-align being lower than that of Hinitial and optimized at a value determined by Bsat/μ of the stamper material (typically≧100 Oe, e.g., from about 2,000 to about 4,500 Oe for the above-listed high Bsat, high μ materials). According to the invention, due to the high permeability μ of the stamper material, the magnetic flux φ provided by the re-alignment field Hre-align tends to concentrate at the projections 18 of the stamper/imprinter 16, which projections are in touching contact with the surface of magnetic recording layer 13′. As a consequence, the surface areas of magnetic recording layer 13′ immediately beneath the projections 18 experience a significantly higher magnetic field than the surface areas at the non-contacting areas facing the depressions 19. If the re-alignment field strength Hre-align is optimized (e.g., as described supra), the direction of magnetization (i.e., alignment) of the perpendicularly oriented magnetic domains 13⊥ will be selectively reversed (as indicated by the arrows in the figure) at the areas of the magnetic recording layer 13′ where the projections 18 of the imprinting surface 17 of the stamper/imprinter 16 contact the surface of the magnetic recording layer 13′, and the magnetic alignment of the perpendicularly oriented magnetic domains 13⊥ facing the depressions 19 in the imprinting surface 17 will be retained. Consequently, upon removal of the stamper/imprinter 16 and the re-alignment field Hre-align in the next (i.e., final) step according to the inventive methodology, a perpendicular recording medium 1′ is formed with a magnetic transition pattern comprising a plurality of reversely oriented perpendicular magnetic domains 13⊥R corresponding to a desired servo pattern.
FIG. 5 illustrates a similar sequence of steps for performing magnetic transition patterning by contact printing of a longitudinal recording medium, e.g., medium 1 depicted in FIG. 1 and comprised of a non-magnetic substrate 10 and an overlying thin layer 13 of a longitudinal-type magnetic layer (where plating layer 11, polycrystalline underlayer 12, protective overcoat layer 14, and lubricant topcoat layer 15 are omitted from FIG. 5 in order not to unnecessarily obscure the essential features/aspects of the present invention) is initially subjected to a magnetic erase (or “initialization”) process for unidirectionally aligning the longitudinally oriented magnetic domains 13=of magnetic recording layer 13. Magnetic initialization of longitudinal medium 1 is accomplished by applying a first, high strength, unidirectional magnetic field Hinitial parallel to the surface of the magnetic recording layer, such that Hinitial≧coercivity of layer 13′ and is typically in the range from about 2,000 to about 20,000 Oe. In this instance, Hinitial is applied perpendicularly (i.e., normal) to the side edges of medium 1, whereas, by contrast, Hinitial for a perpendicular medium would be applied normal to the upper and lower major surfaces of the medium.
According to the next step of the process sequence, a stamper/imprinter 16 comprised of a body of magnetic material having a high saturation magnetization, Bsat, i.e., Bsat≧about 0.5 Tesla, and a high permeability, μ, i.e., μ≧about 5, e.g., selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe, and CoFeV, and having an imprinting surface 17 having a topography comprised of a plurality of projections 18 and depressions 19 arranged in a pattern corresponding to a magnetic transition pattern to be formed in the surface of magnetic recording layer 13, e.g., a servo pattern, is placed in intimate (i.e., touching) contact with the surface of layer 13. A suitable topography for the imprinting surface 17 of a contact mask-type stamper/imprinter 16 for use in forming a servo pattern in longitudinal recording layer 13 according to the invention may comprise a plurality of projections 18 having a height in the range from about 20 to about 500 nm, a width of at least about 0.01 μm, and a spacing (defining the depressions 19) in the range from about 0.01 to about 1 μm. A second, unidirectional magnetic re-alignment field Hre-align parallel to the major surface of magnetic recording layer 13 but of lower strength and direction reverse that of the magnetic initialization field Hinitial is then applied normal to the side edge surfaces of stamper/imprinter 16, the strength of Hre-align being optimized at a value determined by Bsat/μ of the stamper material (typically≧100 Oe, e.g., from about 2,000 to about 4,500 Oe for the above-listed high Bsat, high μ materials). According to the invention, due to the high permeability μ of the stamper material, the magnetic flux φ provided by the re-alignment field Hre-align enters and exits the side edges of the projections and tends to concentrate at the depressions 19 of the stamper/imprinter 16 (rather than at the projections 18). As a consequence, the non-contacted surface areas of magnetic recording layer 13 immediately beneath the depressions 19 experience a significantly higher magnetic field than the surface areas of the magnetic recording layer 13 in contact with the projections 18. If the re-alignment field strength Hre-align is optimized, the direction of magnetization (i.e., alignment) of the longitudinally oriented magnetic domains 13=of the magnetic recording layer 13 will be selectively reversed (as indicated by the arrows in the figure) at the areas facing the depressions 19 of the imprinting surface 17 of the stamper/imprinter 16, whereas the alignment of the longitudinally oriented magnetic domains 13=of the magnetic recording layer 13 in contact with the projections 18 of the imprinting surface 17 of the stamper/imprinter 16 will be retained. Consequently, upon removal of the stamper/imprinter 16 and the re-alignment field Hre-align in the next (i.e., final) step according to the inventive methodology, a longitudinal recording medium 1 is formed with a magnetic transition pattern comprising a plurality of reversely longitudinally oriented magnetic domains 13=R corresponding to a desired servo pattern.
Present magnetic patterning apparatus are comprised of magnet means with variable spacing between poles, and, as a consequence, whenever a stamper/imprinter+media combination is inserted in the inter-polar space for performing magnetic patterning by contact printing, steps for actuation of the magnet, adjustment of the pole gap, and tuning of the magnetic field to a desired intensity must be performed. However, inasmuch as the steps for performing magnet actuation, pole gap adjustment, and magnetic field tuning are time consuming, obtainment of high product throughput rates is disadvantageously compromised by use of existing methodology and equipment. Further, current contact printing apparatus employ electromagnets which are powered by a DC current source, and as a consequence, active cooling of the magnet assembly is required to prevent overheating. Moreover, obtainment of increased magnetic field strengths from such DC powered electromagnets for reducing processing time and increasing product throughput rates disadvantageously incurs very high power consumption rates, hence increased processing cost.
Accordingly, there exists a need for methodology and means for performing servo patterning by contact printing which is free of the above-described drawbacks and disadvantages arising from the requirement for performing time-consuming actuation of the magnet, adjustment of the pole gap, and tuning of the magnetic field to a desired intensity each time a stamper/imprinter+media combination is inserted in the contact printing apparatus in the space between the magnet poles. Moreover, there exists a need for methodology and instrumentalities for performing rapid, cost-effective servo patterning of thin film, high areal recording density magnetic recording media which do not engender the above-stated concerns associated with existing methodologies/instrumentalities for patterning of magnetic media utilizing DC-powered magnet assemblies.
The present invention addresses and solves the above-described problems, disadvantages, and drawbacks associated with prior methodologies for servo pattern formation in thin film magnetic recording media, while maintaining full compatibility with the requirements of automated magnetic hard disk manufacturing technology.